Bears were mysteriously missing toes. These scientists cracked the case.

Clayton Lamb didn’t think much of the missing toe at first.

The Canadian biologist was moving a snoozing bear with conservation officers in Fernie, a ski resort town tucked in the mountains of British Columbia. A tourist from Australia stood on a deck nearby, snapping photos of the hulking grizzly.

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The team had tranquilized the animal to haul it away from a manicured lawn when Lamb saw it: A piece of its paw was gone.

Grizzlies lead rough lives, brawling and biting one another. “So the missing toe of one bear wasn’t necessarily a red flag for us,” Lamb said.

But while doing field work for his PhD at the University of Alberta, he later saw another bear without all its digits, in the province’s Elk Valley region. Then another. Then another.

The sample size was small – four bears. But the pattern was unmistakable. Why were so many bears missing so many toes?

“We had absolutely no idea,” said Lamb, now a postdoctoral fellow at the University of British Columbia. “And we had, at the time, essentially no leads as to what it could be.”

The discovery sent Lamb on a half-decade quest to unravel the mystery of the missing bear toes. The pursuit would not only divert him from his PhD work on grizzly reproduction and survival but would lead him to press for public policy changes.

“Part of what makes a grizzly bear a grizzly bear is their very long claws,” he said. “It’s just something essential.”

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From their muscular shoulders to their huge paws, grizzlies are built for digging.

The bears tunnel underground to build dens and to search for roots, rodents and other morsels to eat. The grizzly’s pronounced shoulder hump is one of the easiest ways tell it apart from a black bear. A grizzly without intact paws simply can’t eat or hibernate as well.

The first question for Lamb’s team: Are some grizzlies simply born this way? Veterinarians who reviewed the paws quickly ruled out any birth defects. X-ray images showed bone fragments, a sign of a wound that had healed.

So something had torn them off. The fractures were too straight and clean for the toes to have been bitten or ripped off by another animal. The linear breaks suggested a human cause.

Lamb’s team turned to traps. Every winter in British Columbia, trappers set hundreds of mousetrap-like devices baited and fastened to trees to capture and kill bushy-tailed, weasel-like animals called martens for their fur. Growing up in the province, Lamb used to trap for beavers, otters and raccoons with his cousin.

To see if bears were too inquisitive for their own good, Lamb installed motion-sensor cameras near four traps that were rigged to remain open, to prevent any further grizzly injuries.

Within two weeks, grizzlies visited all four traps, tripping two of them. Asking around, Lamb heard reports from hunters and trappers from as far as Wyoming and Finland of brown bears getting their feet caught in traps meant for smaller mammals.

But could a trap meant for such a tiny creature really hurt a grizzly? Lamb’s team hooked up a dead bear’s paw to a trap attached to his pickup truck to see how much force it would take to break a toe.

“I did a number of things that I never thought I was going to do as a scientist,” he said.

The traps weren’t strong enough to sever a bear toe right away, Lamb and his team wrote in a paper published in August in the Wildlife Society Bulletin. But Lamb’s team showed the devices could cut off the circulation of blood, causing tissue to die and drop off – eventually.

“It’s fair to assume that there’s quite a bit of suffering over the weeks or months that these toes are actually falling off,” Lamb said. “It’s not an instant thing.”

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The missing toes aren’t a big enough issue to cause a population decline, according to Luke Vander Vennen, a wildlife biologist for the province who collaborated with Lamb in the grizzly research.

But the lost digits are “certainly not the kind of outcome that we’re comfortable accepting as the regular course of business.”

Amputated toes aren’t just bad for bears. They could have consequences for people living in bear country, too.

One of the four bears Lamb found without all its digits was later captured by conservation officers after wandering onto a farm. Another was killed after breaking into a calf pen on a ranch. And a third is suspected of attacking a human.

Bears that get caught in traps may just be more curious to begin with. Or, Lamb said, injured bears without the full use of their paws to dig for meals may take more risks in pursuit of food.

One solution would be to ban trapping in November, when many grizzlies are still active. But some in the fur business worried that delaying trapping until the deep winter would be dangerous because of the risk of avalanche in bear country.

“That would be a fairly blunt instrument to a problem that we can likely solve with a bit more of a nuanced approach,” said Doug Chiasson, executive director of the Fur Institute of Canada, which represents and set standards for trappers.

Another idea for keeping bear claws intact is to place a plate on the traps with an opening big enough for a marten to squeeze through but too small for a grizzly’s foot.

Based on Lamb’s work, trapping licenses in southeast British Columbia started requiring these constraints in recent years. The measure, he said, is “a stopgap as we work on a few more options.”

For Tim Killey, a trapper who leads the British Columbia Trappers Association, another trade group, preventing bears from being ensnared is important for the industry to keep its “social license” in the face of anti-fur sentiment.

“It’s the ethical thing to do,” he added.

Right now, it’s tough to know whether the requirements are working, said Vander Vennen, who used donated lumber to build about 100 boxes himself.

“They’re not hard to build. Once you get set up to do them, then they can go pretty quick.”

So far, he added, no new bears have come in with missing toes.